Automobiles and other vehicles are generally provided with electronic indicating panels on dashboards and the like which are controlled by driving circuits. These vehicles are similarly equipped with audio systems which have respective electronic indicators used for tuning, station identification, volume control and similar adjustments by the user.
These electronic indicators have typically been provided with means to adjust the intensity of the illuminating lamp or lamps in accordance with the ambient lighting conditions, the running condition of the vehicle and the user preferences. For example, when the vehicle is being operated in areas of high external illumination such as in urban districts, it may be desirable to increase the intensity of illumination of the illuminating lamp or lamps, so that the visibility of instruments may be increased. Similarly, when the vehicle is operated on less frequently travelled routes, it may be desirable to decrease the intensity of illumination of the illuminating lamp or lamps to prevent distraction or fatigue to the operator or user.
Several prior art devices have been developed which permit a vehicle operator to control the intensity of illumination of indicator lights based on specific input signals.
U.S. Pat. No. 4,968,917 issued to Harris discloses an electronic dimmer circuit that controls the brightness level of a display device. The Harris patent is specifically directed to the manipulation of output dimming signals. In Harris, a rheostat is used to control the brightness level. In doing so, two dimming reference voltages are generated, LR1 and LR2, with the difference between the two voltages defining an acceptable voltage window. Using a D-to-A converter/microprocessor feedback system, the Harris circuit senses the output of the D-to-A converter and determines if the voltage level falls within the window. If so, an appropriate dimming signal is sent to the driver display which controls the brightness of the display. If the D-to-A signal does not fall within the window, the microprocessor steps down the D-to-A output until the signal falls within the window. Harris' circuit, unlike the present invention, does not engage in statistical analysis, but instead senses the logic condition of a dimming output signal and adjusts the signal level so as to fall into a certain acceptable voltage window corresponding to a certain level of brightness.
U.S. Pat. No. 4,368,406 issued to Kruzich, et al., discloses a lamp dimmer control utilizing a variable resistor and an associated adjustment mechanism having an ambient light sensor. As disclosed by Kruzich, the sensor is mounted integral to the control so as to receive ambient light external to the control housing through a translucent adjustment mechanism. The sensor is utilized in conjunction with the variable resistor to provide information to pulse width modulation circuitry and to maintain a relatively constant illumination contrast with respect to the ambient light levels.
U.S. Pat. No. 4,321,509 issued to Miyaji, et al., also discloses a dimmer to control the intensity of illumination of a lamp or lamps for illuminating an instrument panel. Miyaji further discloses the use of sensing means comprising a varistor to sense and absorb undesirable surge voltages. In operation, the surge voltage sensor acts to shut off a dimming transistor to prevent transmission of high currents which may damage the dimmer.
U.S. Pat. No. 4,891,828 issued to Kawazoe discloses a voltage to pulse-width conversion circuit for adjusting the brightness of electronic indicating devices. As disclosed by Kawazoe, the voltage to pulse-width conversion circuit converts a PWM input signal into a PWM output signal having a predetermined duty ratio. The circuit comprises a counter which counts a reference frequency signal to produce a multi-bit digital value, a digital/analog converter (D/A converter) which converts the digital value into an analog signal, and a voltage comparator which compares the analog output signal of the D/A converter with a control signal for pulse-width modulation to produce a modulated output signal which has a predetermined duty ratio. As disclosed, Kawazoe's circuit is utilized to increase the accuracy of the PWM output signal and thus permit the use of smaller integrated chips.
U.S. Pat. No. 4,358,713 issued to Senoo, et al., discloses a brightness control device for the light emitting display of an automotive vehicle electronic meter. According to Senoo, the brightness of the display is controlled in response to an output pulse signal (having a variable duty factor) produced by an illumination controller. The apparatus disclosed by Senoo permits the brightness of the light emitting display to be properly controlled in response to the ambient light level so as to increase visibility of the display during the day and at night.
U.S. Pat. No. 4,661,717 issued to Nishioka discloses a load condition determining apparatus to determine normal and abnormal conditions of a load circuit. In operation, the apparatus supervises or monitors operating conditions of different lights and lamps, such as headlights, tail lamps and brake lamps and to detect any abnormal conditions such as any short circuit or disconnection of the lights and lamps.
U.S. Pat. No. 4,358,714 issued to Sechler, et al., discloses a light dimming system for simultaneously controlling the brightness of a plurality of two-terminal indicating lights, each having one terminal connected to receive a constant voltage relative to ground. This voltage is arbitrarily variable between predetermined high and low values, to control the intensity of a light connected between the output of the dimmer apparatus and a constant voltage source.
The conventional prior art devices discussed above provide a general background with respect to the control and application of dimming circuits. Significantly, each of the devices operate according to specific input information. These conventional dimming devices therefore suffer from lack of interchangeability in that they are source specific and will only operate in response to particular input unless modified accordingly.
While interchangeability may not have been a significant issue in the past, our new global economy now dictates the use of standard parts which may be interchanged as necessary for use in different applications at multiple manufacturing facilities.
For example, audio systems which are required to be installed in different model automobiles have previously utilized general dimming circuits which must be individually modified prior to installation. More specifically, these prior art systems require modification so as to receive and operate according to the different input signals provided on the lamp lines of the applicable automobile dimming circuits.
For example, in the case of domestic automobiles, a DC (direct current) voltage in the range 0 to 14 volts is typically supplied on the lamp supply line, and the lamp return line is grounded. In contrast, foreign manufactured automobiles have generally utilized pulse-width modulated (PWM) input signals in the range 0 to 14 volts. These automobiles may supply an input signal on the lamp supply line with the lamp return line grounded. Alternatively, a voltage input may be provided on both the lamp return line and the lamp supply line.
As set forth above, conventional dimming circuits require modification when used in different vehicles to operate in accordance with the desired input. Typically, these modifications include the installation or removal of trapping jumpers and related electronics. As readily seen, this approach requires additional assembly time, training, testing and associated costs.